In 1894 Sanderson Brothers Steel Company of Syracuse used the brand name "Sanderson Bros. & Co." with C.H. Halcomb as president & treasurer, W.F. Belknap as secretary and selling agents Hawkridge Brothers of Boston as well as D.G. Gautier & Co. of New York.
D.G. Gautier & Company, selling agent of Sanderson Brothers & Co. with some relationship to the Talcony Steel Company(
http://www.workshopoftheworld.com/tacony/tacony_ordnance.html)
http://books.google.com/books?id=TX0DAAAAYAAJ&pg=PA116-IA8&lpg=PA116-IA8&dq=d.g.+gautier+%26+co.&source=bl&ots=4WV4Coxx4e&sig=NJJWSmpibDdiPAeK7fZBo9n3jm0&hl=en&ei=jhPCS7SrFsX_lgfMx8GJAg&sa=X&oi=book_result&ct=result&resnum=2&ved=0CAoQ6AEwAQ#v=onepage&q=d.g.%20gautier%20%26%20co.&f=false
By the way an Edmund Leavenworth French, born on Ocotber 12th of 1870 in NY City, who attended the Royal School of Mines in Freibert, Saxony of Germany looks to be an intergral part of the Sanderson Brothers & Co., as well as the Crucible Steel Company of America.
So just a wild, wild guess could C, G, & T, as I don't have anything for P(Park Steel Company but connection to S B & Co.?? but were into special steels at the time the Crucible Steel Company absorbed them or Park Brothers with "Black Diamond" trademark? from 1902), be for:
C - Crucible Steel Company
G - Gautier
T - Talcony; with these letters being the facility or company where the steel was sourced? This is all based on the assumption that "S B & Co." would be the brand stamp of Sanderson Brothers & Co.
Kind Regards,
Raimey
rse
